How to externalize the SOLR instance which comes with Alfresco 4.x

Alfresco 4.x uses SOLR instead Lucene. In fact SOLR is just a Lucene index with a service on top of it. Furthermore it provides meanwhile some new features (search facettes, joins, ...) If you install Alfresco Enterprise 4.x by using the installation package (bundled with PostgreSQL and Apache Tomcat), then it is already configured to use the bundled SOLR 1.4. The search service is then deployed as a web application to the Tomat servlet container. A better idea is to deploy SOLR to an own Tomcat server which then has its own Java environment and so on. The second Tomcat instance is running on the same server host, but now a little bit more isolated from the Alfresco instance. Here the steps:

1. Make a new directory 'tomcat_solr' in the Alfresco installation directory $ALF_HOME
2. Copy the contents of the folder 'tomcat' to the folder 'tomcat_solr'
3. In 'tomcat_solr/webapps' undeploy the 'share' and 'alfresco' applications, by removing the folders. Also remove the files 'alfresco.war' and 'share.war' to avoid that Alfresco becomes redeployed.
4.  In 'tomcat_solr/webapps/shared/classes' and 'tomcat_solr/logs' remove everything below it. Also remove 'tomcat_solr/conf/Catalina/localhost/alfresco.xml'. You now have a kind of clean Tomcat instance.
5. Edit the server's configuration by changing the ports. The shutdown port should be '8095', the connector port should be '8090', the SSL port should be '8449', the AJP port should be 8099. You now have a Tomcat instance which does not conflict with the Alfresco one.
6. Open the file 'tomcat_solr/conf/Catalina/localhost/solr.xml'. You can see that the home directory of SOLR is set to 'alf_data/solr'. You can change this if you want to store the index files at another location. Also the SOLR web app archive is stored there.
7. SOLR is configured to use 2 cores. This means that you can find the 2 subfolders 'alf_data/solr/archive-SpacesStore' and 'workspace-SpacesStore'. You can see this maps to Alfresco's content stores. Each SOLR core has its own configuration. In the 'solcore.properties' file you can specify where the index files should be stored. The property 'data.dir.root' points to 'alf_data/solr' for both stores. The 'alfresco.*' settings are used to define which Alfresco instance (host, port, store, interval, ...) is used.
8. More about the keystore is available here  http://docs.alfresco.com/4.1/topic/com.alfresco.enterprise.doc/tasks/generate-keys-solr.html, currently it's just important that you know that your new Tomcat instance is already configured to use the already existing one. It is located under 'alf_data/keystore'. Also the file 'tomcat_solr/conf/tomcat-users.xml' does already contain the required user definition.
9. Finally you need to remove the Solr stuff from the old Tomcat installation, and to change the Alfresco configuration (tomcat/shared/classes/alfresco-global.properties' to use the SSL port which was specified for SOLR (8849). Therefore the property 'solr.port' should be changed. If you also moved the index keystore then you need to change the 'dir.keystore' property.
10. Now start Alfresco!
11. Now start the Tomcat which hosts the SOLR instance. There should be no error in the log file.
12. Log-in to Share, create a new document by setting some attributes.
13. Wait a few seconds (SOLR polls Alfresco!) and then check the log files of SOLR's Tomcat! Afterwards perform a search by using Alfresco Share!